TOPICS: Homocysteine, methylmalonic acid (MMA), megaloblastic anemia, hypersegmented neutrophils, degeneration of the dorsal columns, DNA synthesis, degeneration of spinocerebellar tracts, degeneration of lateral corticospinal tracts, folate supplementation, hematologic symptoms, irreversible nerve damage, cofactor for methionine synthase, microorganisms, veganism, animal products, malabsorption, liver, intrinsic factors, terminal ileum